1. Field of the Invention
An aspect of the present invention relates to at least one of a spectral characteristic acquisition device, an image evaluation device, and an image formation apparatus.
2. Description of the Related Art
In a field of Production Printing, it becomes general to produce prints by an electrophotographic-type or an ink-jet-type printer so that prints are provided as a small batch and in a short delivery time. Then, an image quality similar to that of a conventional offset printing machine is also desired for these printers. Therefore, a color sensing technique for measuring a color at each position of a printed image at a high precision becomes important in order to improve color stability or color reproducibility of an image.
Herein, a spectral characteristic acquisition device capable of acquiring spectral information at 6-31 channels that is more than 3 channels of RGB, calculating a spectral reflectance therefrom, and further calculating color information such as CIE LAB is effective for color sensing at a high precision. Furthermore, a spectral characteristic acquisition device that arrays a plurality of spectrometric sensors in one line, conveys an object to be measured in a direction orthogonal thereto, and conducts sensing in parallel is effective in order to conduct color sensing at a plurality of points on an entire image area.
For one example of such a spectral characteristic acquisition device, it is known that a light beam condensed by a first imaging optical system is spatially limited by an opening sequence such as a slit array, is imaged by a second imaging optical system, and spectrally dispersed by a diffraction element having a diffraction axis in a direction oblique with respect to a direction of arraying of such a slit array.
In such a spectral characteristic acquisition device, spectral characteristics at a plurality of positions are acquired from signals of a plurality of pixels corresponding to respective diffraction images by acquiring spectrally dispersed light beams on a one-dimensional image capturing element (for example, see International Publication No. 02/50783). Because such a spectral characteristic acquisition device uses a one-dimensional image capturing element, a transfer time of an acquired signal is short and a measurement time is short so that it is preferable to measure an image conveyed at a high speed.
Here, a spectral characteristic acquisition device using a two-dimensional image capturing element is unsuitable for sensing of an image conveyed at a high speed, as is required to measure, for example, 1000 times or more for 1 second, because it takes time to transfer an acquired signal.
It is necessary to increase the number of pixels of a one-dimensional image capturing element assigned to each spectrometric sensor in order to provide each spectrometric sensor with a high precision in the aforementioned spectral characteristic acquisition device, however, if so, the number of spectrometric sensors capable of being realized in one one-dimensional image capturing sensor is decreased. That is, there is a trade-off relationship between a precision of each spectrometric sensor and the number of the spectrometric sensors. A case where the number of spectrometric sensors is large is industrially useful, because it is possible to measure a broader range and measure at a higher density.